In situ interfacial surface modification of hydrophilic silica nanoparticles by two organosilanes leading to stable Pickering emulsions

Oil-in-water Pickering emulsions are stabilized by in situ functionalization of hydrophilic silica nanoparticles with two organosilane precursors of opposite polarity, dodecyltriethoxysilane (DTES) and 3-(aminopropyl)triethoxysilane (APTES), in a two-step emulsification procedure. The modification of the silica nanoparticles is verified by Fourier transform infrared (FTIR) spectroscopy analysis. The stabilization of the oil droplets by silica is confirmed by tracing the localization of the colloidal silica nanoparticles at the oil-water interface, as observed by confocal fluorescence microscopy. In comparison to modification of the silica nanoparticles prior to the emulsification, in situ functionalization of silica with both organosilanes achieves enhanced emulsion stability and homogeneity, by forming a polysiloxane network between the silica nanoparticles, through polymerization of the organosilanes in the presence of water. The polysiloxane network fixes the silica in place as solid shells around the emulsion droplets, in structures called colloidosomes. These colloidosome shell structures are visualized using confocal microscopy and cryogenic scanning electron microscopy, the latter method successfully enables the direct observation of the silica nanoparticles embedded in the polysiloxane matrix around the oil droplets. Stabilizing the Pickering emulsion droplets and forming silica-based colloidosome shells is dependent on the extent of the hydrolysis and polycondensation reaction of the two organosilanes.